Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

• the invention relates to an aqueous acidic galvanic zinc bath which, in addition to the usual additives, such as conductive salts and brighteners, contains certain surfactants.
• the electrolytic deposition of zinc on metallic substrates from acidic solution depends on several important criteria. Since the resulting zinc coatings are mostly dull and often irregular from acidic solution, so-called brighteners must be present in the baths in addition to the usual conductive salts (to improve the conductivity of the baths), which give the coatings an increased sheen, and which also allow it to work at lower current densities. These brighteners, which can be assigned to a wide variety of chemical substance classes, are often difficult or impossible to dissolve in water and especially salt solutions, so that certain surfactants have to be added to the baths which serve as emulsifiers, which lead to clear, transparent microemulsions. These measures achieve a uniform deposition of the zinc on the substrates.
• nonionic surfactants have hitherto been used for these purposes, as is known, for example, from GB-PS 1 149 106. Furthermore, from JP-OS 74 89 637 the use of alkyldiphenyloxysulfonic acids is known, the latter of which enable the deposition of relatively uniform zinc layers, but the ductility leaves something to be desired and non-covering coatings result in the low current density range.
• the aim of the invention was to find a class of surfactants which solubilize the brighteners used well and which, from acidic, galvanic zinc baths which contain the usual additives and also water-insoluble brighteners, can be used to obtain uniform and ductile zinc coatings on metallic substrates, even at low current densities.
• the subject of the invention is an aqueous, acidic galvanic bath for the electrolytic deposition of zinc, which contains conductive salts, brightening agents and surfactants, which is characterized by a content of a surfactant of the formula I.
• R 1 is a C 4 - to C 20 -alkyl radical
• R 2 is the radical R 1 or hydrogen
• X and Y is a radical of the formula -S0 3 H
• the hydrogen atom being replaced by an alkali metal, alkaline earth metal atom or an equivalent of zinc can and one of the radicals X and Y can be hydrogen
• n is an integer from 5 to 50
• the compounds of the formula I as a surfactant in aqueous, acidic galvanic baths for the electrolytic deposition of zinc in the presence of brighteners.
• R 1 preferably denotes a C 4 to C 15 alkyl radical. Of particular interest from an industrial point of view are C 4 to C 9 alkyl radicals, of which the butyl, tert-butyl, octyl and nonyl radicals should be mentioned specifically.
• R 2 can have the same meaning as R 1 , preferably R 2 is hydrogen.
• X and Y are preferably the radical -S0 3 H, the hydrogen atom being replaced by sodium or potassium.
• n stands for an integer from 5 to 50, preferably 7 to 30.
• the zinc can be electrolytically used in the bath.
• an alkali metal ion especially the sodium or potassium ion, is preferably chosen as the metal ion.
• the surfactants to be used according to the invention are therefore sulfonated and / or sulfated alkylphenol ethoxylates. They can be used individually or in mixtures with known surfactants. Non-ionic surfactants such as pC 4H9 to C 12 H 25 alkylphenol ethoxylates with 10 to 30 ethylene oxide units or ⁇ -naphthol ethoxylates with 5 to 20 ethylene oxide units are particularly suitable as known surfactants. These are expediently used in an amount of 1 to 15 g / l.
• the zinc baths usually contain brighteners.
• the brighteners used can be divided into so-called basic brighteners and top brighteners.
• Polyethyleneimines or their derivatives, for example, are expedient as basic gloss agents.
• the top brighteners are usually poorly or not at all soluble in the aqueous zinc bath. This includes representatives from a wide variety of substance classes, in particular be voted aromatic or heteroaromatic ketones, as described for example in GB-PS 1 149 106, JP-OS 74 89 637.
• R 3 is an aromatic or heteroaromatic radical, preferably an optionally alkyl, halogen or nitro-substituted phenyl or thienyl radical and R 4 is C 1 - to C 6 -alkyl, or crude products containing these compounds, and / or o- Chlorobenzaldehyde.
• the representative class includes:
• benzal acetone is preferred.
• o-chlorobenzaldehyde can be used alone or as a mixture with a compound of the formula II as a brightener.
• the zinc baths appropriately contain brighteners in a total amount of 1 to 10 g / l. They contain lace gloss agents in an amount of 0.1 to 2.0 g / l, preferably 0.1 to 1 g / l.
• the surfactants to be used according to the invention are present in the baths in an amount of 4 to 30, preferably 5 to 15 g / l.
• the baths have the usual compositions. They contain e.g. 50 to 150 g / 1 zinc chloride or the equivalent amount of zinc sulfate, 100 to 250 g / 1 potassium chloride (conductive salt), 15 to 25 g / l boric acid, 1 to 8 g / 1 sodium benzoate and ggi. 1 to 4 g / 1 agent to increase the scatter, such as naphthalenesulfonic acid / formaldehyde condensation products.
• Other baths can also contain 10 to 160 g / l ammonium chloride or sodium chloride. The pH of the baths is usually between 3 and 6.
• the baths according to the invention provide high-gloss and ductile zinc coatings over the entire current density range.
• the sheets used are run for 10 minutes in a Hull cell with 1 ampere at room temperature (approx. 23 ° C).
• an alkylated diphenyl ether disulfonate (commercially available product) was used as the surfactant.
• the cloud point of the bath at 5 g / 1 and 10 g / l surfactant was above 100 ° C.
• test plate was run in the Hull cell with 1 A at room temperature (approx. 23 ° C.) for 10 minutes.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Cosmetics (AREA)

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Publications (3)

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• 1982
  • 1982-12-29 DE DE19823248503 patent/DE3248503A1/de not_active Withdrawn
• 1983
  • 1983-12-20 DE DE8383112804T patent/DE3370835D1/de not_active Expired
  • 1983-12-20 EP EP83112804A patent/EP0115020B1/fr not_active Expired
  • 1983-12-23 US US06/565,217 patent/US4496439A/en not_active Expired - Lifetime

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